1. Field of Invention
The invention relates to a method for channel estimation and the corresponding system. In particular, the invention relates to a method and its system for channel estimation in a wireless local area network.
2. Related Art
The high speed of IEEE802.11g comes from the use of the design of an orthogonal frequency division multiplexing (OFDM) module. The OFDM module design is the same as the one used by IEEE 802.11a. The compatibility comes from the use of 2.4 GHz bandwidth, which supports the old complementary code keying (CCK) module. The CCK module is the same as the one used by IEEE 802.11b. The new protection mechanism follows the standards in the 11 g draft. However, the drawbacks in IEEE 802.11g are the same as IEEE 802.11b. For example, there are only three sets of non-overlapping channels. Both of them are likely to be interfered by cordless phones and microwave ovens. Therefore, the IEEE 802.11g equipment will face the same interference problem as IEEE 802.11b.
The above-mentioned problem occurs in wireless local area network signal transmissions. The electromagnetic waves reflect off obstacles many times. The signal received by the receiving end can be viewed as the overlap of many original transmission signals multiplied by a constant and delayed by a period of time. This effect is called the multiple path attenuation. If it is not properly taken care of, the efficiency of the receiving machine will be reduced. Generally speaking, the receiving machine has an equalization circuit to remove the multiple path attenuated signal. In the existing wireless local area network (WLAN) system, the channel model is extracted from the message contained in a packet preamble. In some WLAN systems, such as IEEE802.11b, the original message sent in the packet preamble is the same. Through a shuffler, the preamble message becomes unknown to the receiving machine. After a multiple path channel, the starting point of the multiple path channel is hard to obtain. However, the starting point of the multiple path channel has to be obtained for some receiving machine channel model computation methods.